Lipids are indispensable ingredients in the food and cosmetics industries, and they are important precursors in the biodiesel and biochemical industries. Many oleaginous microorganisms produce lipids, including the well-characterized yeast Yarrowia lipolytica. 
Oleaginous microorganisms can be easily and cost-effectively grown on large scale, which suggests broad applicability for biodiesel and biochemical production. Microorganisms may also be engineered to produce high-value products for the food and beverage industries. Further, these products are typically sequestered within the microorganisms, which can facilitate their isolation and purification.
Microorganisms produce lipid products at different rates and with different efficiencies. Lipid production in eukaryotic organisms generally proceeds by the oxidation of pyruvate to acetyl-CoA in the mitochondria via pyruvate dehydrogenase and the subsequent export of acetyl-CoA to the cytosol via the metabolic intermediate citrate. Mitochondrial pyruvate oxidation and citrate export results in a net accumulation of reduced nicotinamide adenine dinucleotide (NADH) in the mitochondria. The accumulation of NADH in the mitochondria is suboptimal for lipid production, however, in part because mitochondrial NADH cannot reduce cytosolic ketones, which results in a lower overall lipid yield.
The lipid yield of oleaginous organisms can be increased by the up-regulation, down-regulation, or deletion of genes implicated in a lipid pathway. The successful modulation of enzymes, however, is unpredictable at best. For example, overexpressing the type 2 diacylglycerol acyltransferase from Mortierella alpine in Y. lipolytica has no significant effect on lipid content (U.S. Pat. No. 7,198,937; hereby incorporated by reference).